Serum Procalcitonin to Support Early Triage for Possible Systemic Infection in Patients with Endophthalmitis

Background: Endophthalmitis is an ophthalmic emergency in which early identification of concurrent systemic infection is important for appropriate clinical management, yet this distinction is often challenging at presentation. Methods: We conducted a retrospective cohort study of patients diagnosed with endophthalmitis at a tertiary referral center between 2017 and 2023. Serum procalcitonin (PCT), C-reactive protein (CRP), white blood cell count, and absolute neutrophil count obtained at presentation were analyzed in relation to clinical classification and systemic infection status, with exploratory receiver operating characteristic (ROC) analyses and Decision Curve Analysis (DCA) used to evaluate diagnostic performance and clinical utility. Results: Among 152 patients, serum inflammatory marker levels were significantly higher in patients classified as having endogenous endophthalmitis than in exogenous cases (p < 0.01), with the greatest separation observed for PCT and CRP. In ROC analyses, PCT demonstrated greater discriminatory capacity for concurrent systemic infection than other markers, with a sensitivity of 91.8%, specificity of 97.9%, and an area under the curve (AUC) of 0.964 at an ROC-derived threshold of 0.11 ng/mL. CRP also showed high discriminatory performance (AUC 0.947), whereas white blood cell count and absolute neutrophil count showed lower AUC values. In patients presenting with endophthalmitis and concurrent uncontrolled systemic infection, PCT showed a higher AUC than CRP (0.995 vs. 0.939). Furthermore, DCA demonstrated that a comprehensive model combining inflammatory biomarkers with clinical risk factors provided the highest net benefit for clinical triage. Conclusions: These findings suggest that serum PCT, particularly when integrated into a multidimensional clinical assessment, may serve as a valuable adjunctive tool to support early triage when systemic infection is a concern.